1. Field of the Invention
The present invention relates to a method for inspecting completely sealed packages, such as food and medical consumption articles, for any pinholes.
2. Prior Art
Today, sealed packaging is used for packing a variety of commodities in addition to food and medical consumption articles such as physiological saline to keep their contents in a sterilized state. In the case of food, the presence of pinholes would cause the contents of the package to contact the air, resulting in deterioration or rot. Also, in the case of medical consumption articles, for example, transfusion bottles, the presence of pinholes would cause contamination or deterioration. Thus, the pinhole inspection for these hermetically sealed packages is of great importance. Conventionally, this pinhole inspection would be carried out in the following method. That is, because a hermetically sealed package does not allow an electrode to be penetrated thereinto, for example in the case of food, a metal pin is stuck into a completed package and taken as one electrode so as to serve as an opposed electrode to an external electrode set in contact with the package. In this state, with a high voltage applied between the two electrodes, the hermetically sealed package is inspected for pinholes, and after the inspection, any pinholes are sealed in a different process. However, this inspection method has had a drawback that the inspection process would be complicated, requiring a subsequent process after the closing of the pinholes. A method for pinhole inspection which solves this drawback and which allows a pinhole inspection to be done without damaging the completed hermetically sealed package has been disclosed in, for example, Japanese Patent Application Publication (Kokoku) No. S50-6998. In this method, a food sealed by a package made from an electrically insulating film is sandwiched between a pair of electrodes, and a voltage is applied between both electrodes so as to give a large difference between capacitances that are formed between the individual electrodes and the food, respectively. Then, a current which is generated by a spark between one of the electrodes and the food is detected, by which any pinhole is detected.
When the presence or absence of any pinhole is detected by detecting a current generated by a spark as described above, it would be the actual case in terms of practical work that the presence or absence of pinholes is detected by a change (magnitude) of the detected current. In this case, applying a voltage between the two electrodes that sandwich the hermetically sealed package would cause a leakage current or charging current to necessarily flow regardless of the presence or absence of pinholes. This phenomenon is more likely to occur particularly with higher voltage, and is also affected by weather such as humidity and temperature of the periphery of the inspection object, which forms the atmosphere during the inspection, where the leakage current becomes larger under the conditions of rain or high humidity. Further, there may arise an error to the current at the detection point due to some influence of floating fine dusts or the like. As a result, the decision as to the presence or absence of pinholes by the magnitude of the current could not be free from operation errors such as a decision of the presence of a pinhole notwithstanding the absence of any pinhole.
The present applicant has previously proposed in Japanese Patent Application No. H8-531816 (U.S. patent application Ser. No. 08/782,599, abandoned) an inspection method for a hermetically sealed package which is fully prevented from occurrence of operation errors due to the atmosphere during the pinhole inspection of a hermetically sealed package in which contents such as electrically conductive fluid or powder or food are covered with an electrically insulating film, where the inspection is done by sandwiching the hermetically sealed package between a pair of electrodes and applying a high voltage between the electrodes.
In this proposal, the hermetically sealed package is placed on a support electrode of a specified configuration, such as a grounded electrode plate, with side face portion of the hermetically sealed package put into contact with the support electrode, and a DC high voltage is applied between the support electrode and an electrode put into close contact with or opposed proximity to an inspection-object end portion of the hermetically sealed package so that the contents of the hermetically sealed package are electrically charged. Then, the grounding of the support electrode is released and moreover the electrode put into contact with the inspection-object end portion is grounded, where a discharge current from the inspection-object end portion is detected, by which any pinhole of the hermetically sealed package is detected.
The above method proposed by the present applicant made it possible to confirm the detection of any pinholes of the hermetically sealed package. However, this pinhole detection method would require a sequence of inspection procedure, including such troublesome steps as releasing the grounding of the support electrode or replacing the support electrode with another support electrode made of insulating material.